Polyamide Membrane Top Layer for Fouling Resistance
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Solution Overview
Problem
Existing reverse osmosis and nanofiltration membranes suffer from high fouling tendencies and sensitivity to free chlorine species, limiting their effectiveness and durability in water treatment applications.
Innovation Solution
The membranes consist of a carrier layer, a porous supporting layer of polysulfone or polyethersulfone, a polyamide separating layer with acid chloride groups, and a top layer of functional group-containing polymers such as polyethyleneimine or polyamidamine, which are chemically coupled to the acid chloride groups, forming a hydrophilic and stable coating that reduces fouling and enhances chlorine resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyamide separating layer is used for reverse osmosis or nanofiltration, then high salt rejection and permeability are achieved, but the membrane exhibits high fouling tendency and sensitivity to free chlorine species
Solution Approach 1:
A top layer made of polymer containing functional groups (such as polyethyleneimine, polyamidamine, polypropyleneimine, polyamine, polyetherol, polysaccharide, or chitosan) is applied as an intermediary between the feed stream and the polyamide separating layer. This top layer serves as a protective mediator that reduces fouling by preventing direct contact between contaminants and the polyamide layer, and protects against chlorine degradation by acting as a chlorine-resistant barrier. The functional groups of the top layer are chemically coupled to the acid chloride groups of the polyamide layer, ensuring stable attachment while maintaining the underlying high-performance separation properties.
2Object-affected harmful factors
If the membrane surface is modified to reduce fouling, then fouling resistance improves, but the chemical inertness to free chlorine and structural stability may be compromised
Solution Approach 1:
The membrane is constructed as a composite structure with multiple layers: a carrier layer, a porous supporting layer, a polyamide separating layer with acid chloride groups, and a top layer of polymer containing functional groups. Each layer contributes specific properties - the polyamide layer provides high salt rejection and permeability, while the top layer provides fouling resistance and chlorine stability. The chemical coupling between layers through functional groups (amino, hydroxyl, carboxyl, or sulfhydryl groups) ensures strong adhesion and structural integrity, creating a composite material that combines the advantages of both layers without compromising chemical stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The membranes exhibit improved fouling resistance and chlorine stability with maintained permeability and salt rejection, extending their service life and reducing fouling tendencies significantly.
Implementation Method 1
the functional groups of the top layer are chemically reactively coupled to the acid chloride groups of the polyamide of the actively separating layer
Implementation Method 2
the ions and molecules migrate through the membrane by diffusing through the membrane material. The solution-diffusion model describes this process
Implementation Method 3
the natural osmosis process is reversed with pressure. This allows the molecules of the solvent to migrate against their 'natural' osmotic direction of propagation. The process pushes them into the compartment where solutes are less concentrated
Data Source
AI summary
The invention relates to the field of polymer chemistry and concerns reverse osmosis or nanofiltration membranes, such as those used for process water treatment and seawater desalination. The object of the present invention is to provide reverse osmosis or nanofiltration membranes that exhibit good to very good fouling properties. This object is achieved by reverse osmosis or nanofiltration membranes consisting of a substrate layer on which a porous support layer, a separation layer, and a cover layer are arranged. The separation layer consists of polyamide with acid chloride groups on its surface, and the cover layer consists of a polymer containing functional groups. The functional groups of the cover layer are chemically coupled to the acid chloride groups of the polyamide in the separation layer.The problem is further solved by a process in which at least one cover layer is applied immediately after the separating polyamide layer.